A new release of Windows 7 Service Pack 1 has been leaked and is now available for download in the wild through various illegal third-party sources such as torrent trackers and warez websites.

Windows 7 SP1 Build 7601.171257 made its way out of Redmond indicating that the company is hard at work developing and testing the first upgrade for the last iteration of its Windows client.

The full Build string of the leaked release is 6.1.7601.171257.101210-1930, v.741, revealing that the software giant compiled it on December 10th, 2010.

Of course, as usual, there’s no word from Microsoft either confirming or denying the legitimacy of Windows 7 SP1 Build 7601.171257.

Judging by the little information available with the leaked bits, Windows 7 SP1 Build 7601.171257 is a pre-RTM release, and in this sense nothing more than an interim Build.

Microsoft produces a constant flow of interim Builds of Windows 7 SP1, sometime at the rate of a new Build per day, but the software giant doesn’t share all of them with testers outside the company, although it’s dogfooding (testing internally) all releases.

In this regard, Windows 7 SP1 Build 7601.171257 seems to be nothing more than the evolution of the Release Candidate of the service pack.

Early adopters that are test driving SP1 RC should stick to the official release from Microsoft and not download the leaked bits, as there’s really no way of trusting the sources offering them.

Obviously, the leaked Build 7601.171257 supersedes the official RC 7601.17105, however, the release is still far from RTM.

According to third-party sources, Microsoft has already signed off on Build 7601.17514.101119-1850 which is very close to the RTM of Windows 7 SP1.

Still, the service pack appears that it has yet to be released to manufacturing. Microsoft won’t say when it scheduled the RTM deadline for Windows 7 SP1, but it did reveal that it will deliver the final version of the service pack in the first quarter of 2011.

At the time of this article only the 32-bit version of Windows 7 SP1 pre-RTM Build 7601.171257 had been leaked, with all wave 1 localized versions available.